Japanese Unexamined Patent Application Publication No. 2009-198054 discloses a gas turbine combustor 1 provided with a combustion cylinder 2, a premixing tube 3, and a fuel supply unit 5. The gas turbine combustor 1 is configured to allow the fuel supply unit to supply the fuel to an annular fuel passage 16 along a tangential direction so that the fuel is uniformly injected through an annular nozzle portion 19. The injected fuel is atomized by air from a circumferential air passage 22 that surrounds the nozzle portion, and an axial flow is generated in the combustor. Meanwhile, air flowing inside through holes 25 in a peripheral wall surface of the premixing tube generates a swirl flow that surrounds the axial flow within the combustor. As a result, the flame is retained at a position apart from a top portion of the combustion cylinder so that a heat shield plate 6 is not excessively heated, resulting in improved durability.
U.S. Pat. Nos. 5,735,681 and 5,879,148 disclose the gas turbine combustor configured to sufficiently mix the fuel and air by air of straight flow directed to the combustion cylinder and air of the swirl flow generated by a swirler for the burner that combusts the fuel so as to stabilize the combustion and realize low emission.
The generally employed gas turbine combustor as described above is normally configured to retain the flame generated by combusting the mixture supplied from the premixing tube in the combustion cylinder at the position apart from the top portion thereof in communication with the premixing tube by a predetermined distance so as to prevent the radiation heat of the flame from damaging the combustion cylinder. The distance from the top portion of the combustion cylinder to the flame is called a lift distance.
The radiation heat of the flame varies with type of the fuel in use. Accordingly, the generally employed gas turbine combustor has been designed to balance the swirl air quantity from the premixing tube with the straight air quantity in accordance with the type of the fuel in use so that the flame lift distance has an appropriate length to prevent thermal damage to the device.
Specifically, the number of swirls of the swirler in use, and the shape and structure of the premixing tube are adjusted to set the balance between the swirl air quantity and the straight air quantity to a desired value. Such adjustment of the structure of the respective portions in accordance with the desired lift distance is very complicated and troublesome work, and considerably time-consuming and costly.
Even if the gas turbine combustor is configured to set the lift distance in accordance with the fuel of the predetermined type, there may be the case where the fuel that generates different radiation heat upon combustion has to be used for certain reasons of usage. In such a case, structures of the respective parts of the gas turbine combustor have to be changed to adjust the swirl air quantity from the premixing tube and the straight air quantity for the purpose of setting a different lift distance in response to the change of the fuel type. Specifically, if the lift distance is intended to be shortened, the modification by increasing the swirl air quantity and reducing the straight air quantity will be necessary. Meanwhile, if the lift distance is intended to be extended, the modification by reducing the swirl air quantity and increasing the straight air quantity will be necessary. The aforementioned modifications are far more complicated and troublesome than providing a newly manufactured gas turbine combustor, even more time-consuming and costly.